Radiatively Driven Winds and Aspherical Mass Loss

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Radiatively Driven Winds and Aspherical Mass Loss
Stan Owocki U. of Delaware
collaborators Ken Gayley U. Iowa Nir Shaviv
Hebrew U. Rich Townsend U. Delaware Asif
ud-Doula NCSU
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General Themes

• Lines vs. Continuum driving
• Oblate vs. Prolate mass loss
• Smooth vs. Porous medium
• Rotation vs. Magnetic field

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Radiative force
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Line Scattering Bound Electron Resonance
for high Quality Line Resonance, cross section gtgt
electron scattering
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Optically Thick Line-Absorption in an
Accelerating Stellar Wind
For strong, optically thick lines
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CAK model of steady-state wind
Equation of motion
inertia
gravity
CAK line-force
Solve for
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Wind Compressed Disk Model
Bjorkman Cassinelli 1993
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Wind Compressed Disk Model
Bjorkman Cassinelli 1993
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Wind Compressed Disk Simulations
radial forces only
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Wind Compressed Disk Simulations
radial forces only
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Vector Line-Force from Rotating Star
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Gravity Darkening
increasing stellar rotation
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Vector line-force With gravity dark.
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Effect of gravity darkening on line-driven mass
flux
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Rotational effect on flow speed

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Smith et al. 2002
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Smith et al. 2003
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But lines cant explain eta Car mass loss
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Super-Eddington Continuum-Driven Winds
moderated by porosity
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Continuum Eddington parameter
constant in radius gt no surface modulation
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Convective Instability

• Classically expected in energy-generating core
• e.g., CNO burning gt e T10-20 gt dT/dr gt
  dT/drad
• But envelope also convective where G(r) -gt 1
• e.g., z Pup G1/2 gt M(r) lt M/2 convective!
• For high density interior gt convection efficient
  
• Lconv gt Lrad - Lcrit gt Grad (r) lt 1
  hydrostatic equilibrium
• Near surface, convection inefficient gt
  super-Eddington
• but flow has M L/a2
• implies wind energy Mvesc2 gtgt L
• wouldtire radiation, stagnate outflow
• suggests highly structured, chaotic surface

Joss, Salpeter Ostriker 1973
.
.
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Photon tiring
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Stagnation of photon-tired outflow
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Shaviv 2001
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Power-law porosity
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Effective Opacity for "Blob"
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Porous opacity
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Super-Eddington Wind
Shaviv 98-02

• Wind driven by continuum opacity in a porous
  medium when G gt1

At sonic point
porosity-length ansatz
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Power-law porosity
Now at sonic point
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Results for Power-law porosity model
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Effect of gravity darkening on porosity-moderated
mass flux
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Eta Carina
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Summary Themes

• Lines vs. Continuum driving
• Oblate vs. Prolate mass loss
• Smooth vs. Porous medium
• Rotation vs. Magnetic field

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Wind Magnetic Confinement
Ratio of magnetic to kinetic energy density
for Homunclus, need B104 Ggt
for present day eta Car wind, need B103 G
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MHD Simulation of Wind Channeling
No Rotation
Confinement parameter
A. ud Doula PhD thesis 2002
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Field aligned rotation
A. ud-Doula, Phd. Thesis 2002
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Disk from Prograde NRP
w0.95 DVamp a 25 km/s DVorb
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Azimuthal Averages vs. r, t